BIOLOGY Volume 3 - A Guide to General Biology - 2004

26. EVOLUTION, OR THE HISTORY OF LIFE ON EARTH

26.4. The Theory of Evolution

26.4.2. Darwin, Wallace, and the Origin of Species by Natural Selection

Charles Darwin was born in 1809. The son of a wealthy physician, he showed no particular promise as a scientist in his early years, much like many other great minds. In 1831, he accepted an unpaid position as a naturalist aboard HMS Beagle, a Royal Navy ship embarking on a five-year surveying voyage along the eastern coast of South America. The Beagle returned to Falmouth in October 1836, having charted a course along the shores of Chile, across the Galápagos Islands, Tahiti, New Zealand, Tasmania, and South Africa. While Darwin spent a large portion of this time conducting geological investigations, his five-week stay in the Galápagos Islands drew his attention to the striking similarities between the islands' flora and fauna and those of the mainland. He was particularly intrigued by the distribution of tortoises and finches (Section 26.7.2). Having amassed a wealth of data on organismal variation, he became convinced that species could not be considered immutable.

Following his return to England, Darwin began studying the breeding of pigeons and other domestic animals, which led him to METABOLISM/2.html">THE CONCEPT OF artificial Selection; however, he still could not envision how selection might operate under natural conditions. In 1778, the clergyman Thomas Malthus published his An Essay on THE PRINCIPLE OF Population, which vividly outlined the potential consequences of an unchecked human reproductive potential. Darwin applied Malthus's reasoning to other organisms, noting that despite their high reproductive potential, population sizes remain relatively constant.

Synthesizing a vast body of evidence, Darwin began to realize that under conditions of intense competition among population members, any variations advantageous for survival in a given environment would increase an individual's ability to reproduce and leave fertile offspring. Less favorable variations are disadvantageous, and individuals possessing them are less likely to reproduce successfully. These insights provided the framework for The Theory of evolution by natural selection, which Darwin formulated in 1839, though he chose not to publish it at the time. In essence, Darwin's greatest contribution to science lies not in proving that evolution occurs, but in demonstrating how it can take place.

Meanwhile, another naturalist, Alfred Russel Wallace—who had traveled extensively in South America, Malaysia, and the islands of Southeast Asia, and had also read Malthus—independently arrived at the exact same Conclusions as Darwin.

In 1858, Wallace outlined his theory in a 20-page manuscript and sent it to Darwin. This catalyzed and encouraged Darwin, and in July 1858, Darwin and Wallace presented joint papers on their ideas at a meeting of the Linnean Society in London. Just over a year later, in November 1859, Darwin published On THE ORIGIN OF Species by Natural Selection. All 1,250 copies of the book sold out on the very first day, and it is said that in terms of its impact on human thought, it is rivaled only by the Bible.